Yes, of course Nagaland is safe through the years, there are no ongoing scuffle in Nagaland. But make sure where you are visiting. Keep in mind about these things to make your visit a memorable one without any stress and less problematic. Get the Inner line permit, since Nagaland is situated and shares border with Burma, we require an inner line permit to visit such places. The Cab drivers won't pick you up if you say you don't have pass(innerline permit). You can take your ID card with you if you're any government official, or student that will work as a Pass(Aadhar card won't help) but take your adhar card with you. If you're a private sector employee you can still go if you provide your Icard and tell the policemen at the check post. Usually they are jerks, but they'll listen if you speak properly. They'll listen even carefully if they believe you're from media.